After weeks of waiting, the first untethered jailbreaks for iOS 4.3.1 were released earlier this week. PwnageTool, sn0wbreeze and redsn0w all were updated to include the exploit uncovered by iPhone security expert Stefan Esser about two weeks ago.
However, one popular tool, ultrasn0w, is still lagging, as it was last updated back in November 2010. The Dev Team isn’t resting on its laurels though, as MuscleNerd announced yesterday that an update for the tool was almost ready, and is currently under testing.
Note that the new version of ultrasn0w (version 1.3?) will not allow iPhone users to to unlock new basebands, as at this stage, it will only allow users who already have an unlocked baseband to keep the unlock once they update their device to iOS 4.3.1.

The new version of ultrasn0w should hit Cydia within the next couple of days. Note that the latest version of PwnageTool will allow you to preserve your baseband unlock as well, but the tool will also jailbreak your device, and is only compatible with Macs. The updated ultrasn0w will only allow you to keep your iPhone unlock, but it will be compatible with both Windows and Mac.